In a short range wireless communication or a mobile communication, a microwave band is usually used, particularly the frequency band ranging from 1 GHz to 10 GHz. The communication devices used in these communications are strongly demanded to be downsized and thinned. Also, the electronic component used in the communication devices are also strongly demanded to be downsized and thinned.
The electronic component used in the communication devices includes a component containing a resonator such as a band pass filter. Such a resonator contains a component using a distributed constant line or a component using an inductor together with a capacitor, and each component is provided with a transmission line. In the resonator, the unloaded Q value is required to be relatively high. The unloaded Q value of the resonator can be increased in the resonator by decreasing the loss in the resonator.
The loss in the transmission line includes the dielectric loss, the conductor loss and the radiation loss. The higher the signal frequency is, the more evident the skin effect becomes. Also, the conduct loss will significantly increase. The loss in the resonator almost derives from the conduct loss. Thus, in order to increase the unloaded Q value in the resonator, it will be effective to decrease the conduct loss.
The conventional transmission line for the frequency band of 1 GHz to 10 GHz is one with a structure obtained by combining the conductor and the dielectric. In such a transmission line, it is difficult to decrease the conductor loss to a great extent even if some strategies are applied as described in Patent Document 1 and Patent Document 2. For example, the surface area of the conductor is increased. In this respect, in the resonator using this transmission line, the increase of the unloaded Q value is limited.
On the other hand, the dielectric line is known as a transmission line for transmitting the electromagnetic waves at a millimetric wave band of about 50 GHz. For example, a transmission line has been disclosed in Patent Document 3 which is configured by disposing a tape with a high dielectric constant between two conductor plates parallel to each other and also disposing a filling dielectric made of a material with a low dielectric constant between each conductor plate and the tape with a high dielectric constant. In this transmission line, the electric field of the electromagnetic wave is distributed inside the filling dielectric. It has been described in Patent Document 3 that the actually prepared transmission line has a low dispersing property at the frequency band of 30 GHz to 60 GHz.